Combined variable resistance device and mechanism for driving same



Dec. 10, 1963 M. MCCLAY 3,114,126

commas VARIABLE mssxs'rmcz: mzvxcs AND MECHANISM FOR muvmc sm: Filed April 2. 1962 y 2 Sheets-Sheet 1 mmvron MARVIN McCLAY ATTORNEY Dec. 10, 1963 M. M cLAY 3,114,126

7 COMBINED VARIABLE RESISTANCE DEVICE AND MECHANISM FOR DRIVING SAME Filed April 2 1962 2 Sheets-Sheet 2 0: I Q o N 0 Q 0 (9 a I0 2. 2 2- m I O 0 g l I Z Q U- INVENTOR. MARVIN McCLAY ATTORNEY FIG. 3

United States Patent 3,114,126 CDMBINED VAREABLE RESISTANCE DEVICE AND MECHANISM FOR DRIVING SAME Marvin McCiay, Costa Mesa, Calif, assignor to Beekman instruments, Inc., a corporation of California Filed Apr. 2, 1962, Ser. No. 184,026

g 11 Claims. (Cl. 338-116) This invention relates to a combined variable resistance device and mechanism for driving same and, more particularly, a device of this general description in which the driving mechanism is mounted substantially within the confines of the variable resistance device.

Variable resistance devices, particularly those knownin the art as precision potentiometers, are commonly employed as displacement to voltage transducers in many fields of contemporary endeavor. By way of specific eX- ample, servo loop systems oftentimes includes servo motor driven potentiometers in which the output of the potentiometer provides a voltage indicative of the mechanical rotation of the servo motor. Such an arrangement of com ponents finds wide utility, for example, in airborne and space craft, both vehicles however offering environments in which space utilization and weight are most critical.

It is accordingly, an object of the present invention to provide a combined variable resistance device and mechanism for driving same which requires a minimum amoun of space and weight.

Furthermore, the combined variable resistance device and driving mechanism should be such that a minimum number of structural changes are required in each of these components so as to facilitate manufacture thereof. The provision of such an apparatus is a further object of this invention.

Other and further objects, features and advantages of the invention will become apparent as the description proceeds. I

Briefly, in accordance with a preferred embodiment of the present invention asuitable driving mechanism is coupled to a movable electrical contact carrier assembly. Suitable driving assemblies are presently available requiring little if any structural modification, these components ordinarily including a servo motor mounted within a generally cylindrical housing and a gear reduction device mounted in a generally similar cylindrical housing. Depending upon the size of these components, at least one and possibly both thereof may be mounted within a modified prior art variable resistance housing as described below. The movable contact assembly preferably comprises a generally L-shaped member with the horizontal leg thereof fixedly mounted transverse to the output shaft of the driving mechanism. The vertical leg of the L-shaped member is then located parallel to the shaft and extends closely adjacent the cylindrical housing of the gear reduction apparatus. mounted upon the latter leg and engages a multi-turn helical resistance element which surrounds both the mov able contact carrier assembly and the driving mechanism. A generally cylindrical housing both supports the resistance element and covers all or most of the other components.

Another embodiment of the invention described hereinafter incorporates ganged single-turn resistance elements which are mounted to an outside cylindrical housing and which surround the movable contacts support assembly and the drive mechanism.

When constructed in the manner of this invention, very compact combined variable resistance and drive mechanisms are provided which require little if any additional space over that required by the variable resistance device er se. Moreover, many of the elements utilized in the present invention may be identical or-only slightly modi- An electrical contact is translatably ice fied from those presently employed to construct the individual variable resistance devices, gear reduction units and servo motors. Accordingly, a more compactdevice tion takenin conjunction with the accompanying drawings in which; 7

FIG. 1 is an exploded view of an embodiment of the present invention involving a multi-turn precision potentiometer;

FIG. 2 is a cross-sectional view in which certain parts are shown in elevation, taken at line 2-2 of FIG. 3;

FIG. 3 is an end view of the apparatus of FIG. 1 as assembled;

FIG. 4 is across-sectional view in which certain parts are shown in elevation, taken at line 4-4 of FIG. 5; and

FIG. 5 is an end view of an alternative embodiment of the present invention, involving ganged single-turn potentiometers.

Referring now to FIGS. 1, 2 and 3, the drive mechanism is mounted within a generally cylindrical case or housing 11 including projecting threaded bolts 12 adapted for extending through mating holes 13 of the cover member 14. The drive mechanism will usually incorporate a re- 7 duction gear assembly and, if sulTicient space is available,

an electromotive apparatus such as a servo motor. With the unit shown, it is assumed that there is insufficient room inside the usual potentiometer housing for including both the reduction gear assembly and the servo motor and'as a result the servo motor 15 is shown attached to the outside of the cover 14 by way of a C-type clamping ring 16 engaging an annular groove 17 in the outside wall of the servo motor. Screws 18 extend through suitable hole 19 of the ring 16 and mate with threaded apertures 20 of the cover member 14. The servo motor shaft is formed as a spline gear and extends through the cover 14 into an opening 21 of the reduction gear assembly. A spur gear (not shown) within the opening 21 engages the splined I shaft 25.

The drive shaft 27 of the driving mechanism component 10 is fixedly attached to a movable contact carrier assembly 28. Movable contact carrier assembly 28 includes a generally L-shaped rotor member 29 of which the horizontal leg 30 incorporates a transverse cylindrical bushing 31 attached at one end to the driving mechanism shaft 27 by a roll pin 34 or other suitable means, and at the other end 'to the inner race .32 of ballbearing 33. Attached to and integral with horizontal leg member 30 is a vertical bar 40 located parallel to the shaft 27 and extending proximate the housing of component 11. A contact carrier 42 rides upon this bar for movement substantially parallel to the axis of rotation of the shaft. The bar 40 has fiat walls 48, 49 whilch lie in planes that intersect at a line substantially parallel to the axis of the shaft 27. The

contact carrier 42 has corresponding flat walls for surface engagement with the walls 48, 49 of the bar 40. These walls serve as a guide groove for the contact carrier and preferably converge toward the shaft 27.

A flexible contact '43 for electrically engaging the turns of the helical coil is carried on the contact carrier 42 by suitable means. An external electrical connection is made to the sliding contact 43 through a flexible lead 41, a slip ring wiper 44 and a slip ring 46. Wiper 44 is attached to the rotor member 29 byan insulating member 45. The slip ring 46 includes an elongated tongue 47, an annular section 57 and four ears or tabs 58 extending outward from the periphery of the annular section 57. The slip ring is preferably made from a single flat piece of electrically conducting metal and is mounted in the base of housing 51 by passing the tongue 47 outward through slot in the wall of the housing (not shown) and then pressing the annular section 57 into an annular shoulder formed in the end of the housing (not shown), the cars 58 engaging the inner surface of this shoulder and fixing the slip ring in position.

The contact carrier 42 preferably includes means for engaging the turns of the helical resistance element 50 to advance the carrier along the bar 40 as the contact carrier assembly is rotated. These means may include parallel ribs 55, 56 of insulating material extending outward from the contact carrier for engaging the sides of the turn which is being electrically contacted by the contact 43. The ribs 55, 56 are preferably skewed to the helix angle of the major helix of the resistance element 50 for better alignment with the turns of the coil. This and other details of the contact carrier 42 and slip ring 46 are fully described in Letters Patent of the United States No. 2,887,555 entitled Potentiometer, filed by Gabriel Marason, Jr., and assigned to Beckman Instruments, Inc., assignee of the present invention.

Resistance element 50 preferably comprises a relatively fine wire closely wound in numerous turns on a core, which core in turn is wound in turns to form a second spiral. The resistive wire may be said to have the form of a double spiral in which the turns of relatively small diameter on the core form a minor spiral and the turns of the core of larger diameter form a major spiral.

The second or outer housing 51 preferably comprises a cylindrical portion 60 closed by an end wall 61 (-FIG. 2). The inner surface of the cylindrical portion 60 provides a helical shallow groove into which is expanded the helical resistance element 50. One or both ends or other taps of the resistance element may be connected to external terminals on the outer surface of the cylindrical portion 60. In the construction shown, two such terminals 52, 53 are provided. The end wall 61 fixedly retains the outer race 54 of bearing 33, thereby rotatably supporting the movable contact carrier assembly.

The open end of the housing is closed by the cover 13 secured to an annular ring 62 by three bolts 63 passing through openings 64 of the cover (FIG. 2). Ring 63 is retained in an annular groove 65 formed in the inner surface of the cylindrical portion 60 near the open end of the housing 51. Additional details of the housing and cover may be found in the aforementioned Leters Patent of the United States No. 2,887,555.

-In operation, the drive mechanism 10 causes the movable contact carrier assembly to rotate about the axis defined by shaft 27, the bearing 33 and the bearings of the drive mechanism. The electrical contact 43 is thereby caused to slidably engage the resistance element 51 and follow the turns of its major spiral. .The resistance between either of the contacts 52, 53 and the contact formed by the elongated tongue 47 of the slip ring 46 is a precise indication of the angular position of the output shaft 27 of the drive mechanism 10.

It will be apparent from the foregoing description that the present invention affords a very compact variable resistance device and mechanism for driving the movable contact carrier assembly since the component 10 is located completely inside and is surrounded by the movable contact carrier assembly and the resistance element. Moreover, the total weight of the completed device is substantially the same or even less than the combined weight of the individual components.

In FIGS. 4 and is shown another embodiment of this invention incorporating two single-turn variable resistance elements. As shown, a generally cup-shaped housing '73 includes a cylindrically member 74 connected to a generally cup-shaped member 75 having a cylindrical portion 76 and an end wall portion 77. A driving mechanisrn 7 8 is fixedly mounted to the end wall portion. This driving mechanism may incorporate a servo motor, a servo motor and geanhead, or as shown in FIG. 4, a gearhead coupled to an externally located servo motor 79 also attached to the end wall 77. The output shaft 85 of the driving mechanism 78 is affixed to a thin wall cylinder 80 having an end wall 81. The end 81 includes an extending bushing 82 which is afixed to the shaft 85 by a roll pin $3. Cylindrical member 80 may, for example, be constructed of stainless steel having a layer of insulating material such as an epoxy plastic upon its outer surface.

An annular conductive ring 99 is located upon the outer surface of cylindrical member 89 proximate each of the single-turn resistance elements. These rings may be constructed of a brass which has been hard gold plated and provide a slip ring electrical contact for the movable contact 1 connected thereto. A generally V-shaped groove in each of the conductive rings is engaged by a conductive wire spring contact 92. Each of these conductive wire contacts are connected to an external terminal 94 extending outwardly from the outer surface of the housing 73. The movable contacts 91 engage the single-turn resistance elements 93 fixedly retained to the inner surfaces of the respective cylindrical portions 74-, 76. These resistance elements may, for example, comprise a single-turn of a circular mandrel or core upon which are wound a number of turns of relatively small diameter resistance wire. As shown in FIG. 5, external terminals 95, 96 are ordinarily connected to respective ends of these of the resistance elements.

In operation, the driving mechanism 78 causes the cylinder 80 to rotate about its cylindrical axis thereby slidably engaging each of the movable contacts 91 with its associated single-turn resistance element 93.

Although an exemplary embodiment of the invention has been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow.

I claim:

1. A variable resistance device comprising:

a gear reduction apparatus mounted within a first housing and having a driven shaft extending therefrom;

a movable contact carrier assembly comprising a base element located transverse said shaft and fixedly mounted thereto,

a grooved cantilever bar having one end mounted integral with one end of said base element, said bar being located parallel with said shaft and extending proximate the housing of said gear reduction apparatus, and

a movable electrical contact means having a support slidabl-y engaging the groove in said cantilever bar;

a hollow second housing having a helical groove formed in its inside wall;

a multi-turn helical resistance element supported in said groove and in engagement with said electrical contact means, said element surrounding said gear reduction apparatus and said movable contact carrier assembly so that its helical ax-is coincides with the rotational axis of the driven shaft of said gear reduction apparatus; and

guide means on said movable electrical contact means associated with said helical resistance element for moving said contact means along said grooved cantilever bar as said movable contact assembly is rotated.

2. A variable resistance device comprising:

a gear reduction apparatus mounted within a first housing and having a driven shaft extending therefrom;

a movable contact carrier assembly coupled to and being rotatably driven by said driven shaft, said assembly including a contact support member located substantially parailel to said driven shaft and extending proxsaid contact support member comprises a generally L-shaped rotor having a base element located transverse said driven sha-ft and fixedly mounted thereto and a bar having one end mounted integrally with one end of said base element, said bar extending substantially parallel with said shaft and extending proximate the cylindrical housing of said gear reduction iappparatus, said electrical contact means being carried by said bar. 4. The variable resistance device defined in claim 3 wherein:

said housing is provided with oppositely disposed end walls said driving mechanism is fixedly mounted to the interior of one end wall of said second housing; and said horizontal member of said L-shaped rotor includes a bushing rotatably mounted in [the opposite end wall of said housing. 1 5. The variable resistance device defined in claim 3 wherein:

said electrical contact means is slidably mounted upon said bar. 6. The variable resistance device defined in claim 5 wherein:

said resistance element comprises a multi-turn helical resistance element in engagement with said electric-al contact means, said element surrounding said driving mechanism and said movable contact carrier assembly so that its helical axis coincides with the rotational axis of the driven shaft of said driving mechanism.

7. The variable resistance device defined in claim wherein:

said movable contact carrier assembly comprises a generally cylindrical member fixedly mounted to and grooved annular conductive members fixedly attached 9 to the outside surface of said cylindrical member adjacent respective ones of said ganged single-turn resistance elements; said electrical contact means comprising at least one electrical contact fixedly mounted to each of said annular conductive members and engaging a respective one of said single-turn resistance elements; and spring contacts carried by said second housing in slipring engagement with respective ones of said grooved annular conductive members. 25 10. The variable resistance device defined in claim 2 wherein said second housing comprises:

a generally cylindrical member supporting said resistance element upon the inside surface thereof, said second housing having an end cover fixedly from the interior surface thereof.

11. The variable resistance device defined in claim 10 including:

a servo motor attached to the outside surface of said mounting said gear reduction apparatus extending I 

1. A VARIABLE RESISTANCE DEVICE COMPRISING: A GEAR REDUCTION APPARATUS MOUNTED WITHIN A FIRST HOUSING AND HAVING A DRIVEN SHAFT EXTENDING THEREFROM; A MOVABLE CONTACT CARRIER ASSEMBLY COMPRISING A BASE ELEMENT LOCATED TRANSVERSE SAID SHAFT AND FIXEDLY MOUNTED THERETO, A GROOVED CANTILEVER BAR HAVING ONE END MOUNTED INTEGRAL WITH ONE END OF SAID BASE ELEMENT, SAID BAR BEING LOCATED PARALLEL WITH SAID SHAFT AND EXTENDING PROXIMATE THE HOUSING OF SAID GEAR REDUCTION APPARATUS, AND A MOVABLE ELECTRICAL CONTACT MEANS HAVING A SUPPORT SLIDABLY ENGAGING THE GROOVE IN SAID CANTILEVER BAR; A HOLLOW SECOND HOUSING HAVING A HELICAL GROOVE FORMED IN ITS INSIDE WALL; A MULTI-TURN HELICAL RESISTANCE ELEMENT SUPPORTED IN SAID GROOVE AND IN ENGAGEMENT WITH SAID ELECTRICAL CONTACT MEANS, SAID ELEMENT SURROUNDING SAID GEAR REDUCTION APPARATUS AND SAID MOVABLE CONTACT CARRIER ASSEMBLY SO THAT ITS HELICAL AXIS COINCIDES WITH THE ROTATIONAL AXIS OF THE DRIVEN SHAFT OF SAID GEAR REDUCTION APPARATUS; AND GUIDE MEANS ON SAID MOVABLE ELECTRICAL CONTACT MEANS ASSOCIATED WITH SAID HELICAL RESISTANCE ELEMENT FOR MOVING SAID CONTACT MEANS ALONG SAID GROOVED CANTILEVER BAR AS SAID MOVABLE CONTACT ASSEMBLY IS ROTATED. 